1. Technical Field
This invention relates to devices for insufflating gas into a mass of molten metal.
2. Description of the Prior Art
Prior structurs of this type have generally employed permeable plugs through which the gas is introduced into the molten metal. Such typical devices may be seen in U.S. Pat. Nos. 2,811,346, 3,330,645, 3,610,602, 3,834,685 and 4,053,147. In all of these prior art devices, the gas must flow upwardly through a gas permeable body which in U.S. Pat. No. 3,811,346 is a porous refractory material. The same porous material is disclosed in Patent 3,330,645 and this patent additionally proposes to form tubular passageways through the porous material. The body of the device in U.S. Pat. No. 3,610,602 is formed of permeable refractory as is the body of the device shown in U.S. Pat. No. 3,834,685 and the same is true of the body of the device shown in U.S. Pat. No. 4,053,147.
French Pat. No. 2,451,945 has a porous stopper plug as has U.S. Pat. No. 3,208,117.
The present invention comprises an improvement with respect to my U.S. Pat. Nos. 4,396,179 and 4,483,520 wherein a non-permeable refractory plug is disclosed having a spaced stainless steel jacket thereabout forming an annular passageway through which the gas is introduced into the molten metal. A displaceable cap is provided in these devices for initially protecting the upper end of the device and the annular gas passageway from being plugged by molten metal introduced into the ladle in which the device is positioned.
In actual practice, it has been determined that the cap is frequently displaced by the molten metal and the molten metal tends to plug the annular gas passageway unless a substantially higher gas pressure is employed to move the molten metal away from the annular gas emitting opening.
Furthermore, the molten metal first introduced into a ladle equipped with the device tends to freeze almost instantaneously and frequently before the gas is introduced or during the initial introduction of the gas and thus closes the annular gas passageway and renders the device ineffective.
The present invention adds a hot metal dam above the annular gas emitting passageway of the device and protects the passageway and the upper portion of the device from the molten metal whether the gas is flowing or not and when the gas flows, it improves the stirring action sustantially by forming a large and distinct and jet-like stream of the gas bubbles which result in increased turbulence and stirring action in the molten metal.